The investigation of subterranean formations is a common occurrence in oil and gas exploration and production operations. Methods and tools for investigating subsurface formations have advanced considerably over the years. There are many commercially available acoustic, nuclear, electromagnetic, and resistance tools that provide a variety of information about formations adjacent to a borehole. For example, some recent wireline sonic logging tools can achieve full formation characterization.
For sonic logging tools, one of the important improvements in formation evaluation has been the increase in the number receivers and transmitters. Some current sonic logging tools have dozens of receivers or more, which are located both longitudinally and azimuthally around a receiver sonde. In addition, some sonic tools include multiple monopole and dipole sources, each capable of firing pulses at different frequencies. These advances in hardware have proven important for a better understanding of formations surrounding boreholes, especially for complex environments such as altered or anisotropic formations. Such complex environments require the collection and transmission of very large amounts of data.
However, the tradeoff for better formation evaluation during recent years is reduced logging speed. Transmitting large amounts of data often requires a decrease in logging speed. Communication bandwidth is limited, especially in a subterranean measurement environment. Therefore, the limiting factor in many subterranean measurement operations is the communication capability. Accordingly, in order to send the large amounts of data generated by recent formation measurement systems, slower measurement-taking speeds are required, and slower measurement-taking speeds result in longer operations and increased rig time. Longer operations and increased rig time result in additional expenses. Consequently, there is a need for data compression methods and systems to enable more efficient communication between subterranean measurement tools and surface apparatus.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems outlined above.